getMarket message with no token specified causes an exception

[freeatnet]

Steps to reproduce:

1. Use a client to send FD WS API a getMarket message with no token specified.

Expected: Server replied with an empty or generic market event.
Observed: No response; exception thrown.

Relevant logs:

websocket_server_1     | 2018-02-14T21:22:15.418806190Z Traceback (most recent call last):
websocket_server_1     | 2018-02-14T21:22:15.418809016Z   File "/usr/local/lib/python3.6/site-packages/engineio/asyncio_server.py", line 266, in _trigger_event
websocket_server_1     | 2018-02-14T21:22:15.418811654Z     ret = await self.handlers[event](*args)
websocket_server_1     | 2018-02-14T21:22:15.418823629Z   File "/usr/local/lib/python3.6/site-packages/socketio/asyncio_server.py", line 364, in _handle_eio_message
websocket_server_1     | 2018-02-14T21:22:15.418826453Z     await self._handle_event(sid, pkt.namespace, pkt.id, pkt.data)
websocket_server_1     | 2018-02-14T21:22:15.418828694Z   File "/usr/local/lib/python3.6/site-packages/socketio/asyncio_server.py", line 294, in _handle_event
websocket_server_1     | 2018-02-14T21:22:15.418831039Z     await self._handle_event_internal(self, sid, data, namespace, id)
websocket_server_1     | 2018-02-14T21:22:15.418833395Z   File "/usr/local/lib/python3.6/site-packages/socketio/asyncio_server.py", line 297, in _handle_event_internal
websocket_server_1     | 2018-02-14T21:22:15.418835719Z     r = await server._trigger_event(data[0], namespace, sid, *data[1:])
websocket_server_1     | 2018-02-14T21:22:15.418837877Z   File "/usr/local/lib/python3.6/site-packages/socketio/asyncio_server.py", line 325, in _trigger_event
websocket_server_1     | 2018-02-14T21:22:15.418840075Z     ret = await self.handlers[namespace][event](*args)
websocket_server_1     | 2018-02-14T21:22:15.418842214Z   File "/usr/src/app/app/services/websocket_server.py", line 241, in get_market
websocket_server_1     | 2018-02-14T21:22:15.418844449Z     "buys": [format_order(order) for order in orders_buys],
websocket_server_1     | 2018-02-14T21:22:15.418846717Z UnboundLocalError: local variable 'orders_buys' referenced before assignment